A hybrid electric vehicle uses two or more different kinds of power sources, which are an engine that obtains a driving torque by burning fuel and a motor that obtains a driving torque with battery power.
The hybrid electric vehicle can provide optimum output torque, depending on how the engine and the motor operate while the vehicle is driven by the two power sources, that is, the engine and the motor.
The hybrid electric vehicle has an exhaust gas recirculation (EGR) system that recirculates exhaust gas into a combustion chamber to reduce fuel consumption.
The hybrid electric vehicle controls a brake mean effective pressure of the engine as a high level to improve fuel efficiency, and applies an Atkinson cycle to intake and compression processes. Thus, a pressure of an intake manifold may be controlled as a high level compared to a general engine vehicle.
In addition, when the exhaust gas is recirculated from an exhaust line to an intake line, a throttle valve can be opened even more due to inflow of fresh air, thereby the pressure of the intake manifold may be increased more.
Therefore, a pressure difference between a front side and a rear side of the exhaust gas recirculation valve is generated, such that stability of controlling an opening of the exhaust gas recirculation valve may be decreased.
Further, when the EGR valve is closed to solve the above problems, fuel consumption may increase and quality of exhaust gas may be deteriorated.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention, and therefore, it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.